The present invention relates generally to communication systems for transmitting and receiving data in conjunction with a broadcast television signal and more particularly concerns the transmission and reception of data in subscription television systems.
ln subscription television systems, television signals are typically transmitted to system subscribers in a scrambled form either along a coaxial cable or as an "over-the-air" broadcast. Each system subscriber is provided with a decoder operable for unscrambling the transmitted television signal and for supplying the unscrambled signal to a conventional television receiver for viewing. ln addition, many present-day subscription television systems are addressable in nature whereby the operation of individual decoders may be selectively controlled through the transmission of system control data generated at the system head-end. The system control data may include such information as subscriber address codes, subscriber authorization codes, program codes and the like enabling the system operator to designate different levels or tiers of programming authorized for different individual subscribers.
Various techniques are known in the industry for transmitting such system control data in conjunction with a television signal. These known techniques, however, are normally limited in the amount of data which can be transmitted in a reasonable time frame and typically reguire the use of re1atively complex and therefore expensive data encoding and decoding apparatus.